An AFX zeolite is a small-pore zeolite having 8-membered oxygen rings. This is used as a catalyst exhibiting high activity in an MTO (methanol to olefins) reaction. In recent years, AFX zeolites have been highly anticipated as zeolites suitable for a catalyst used in selective catalytic reduction (referred to as “SCR” hereafter), wherein nitrogen oxides are reduced and detoxified. Such a catalyst is referred to as “SCR catalyst” hereinafter.
Incidentally, zeolite is difficult to predict and design, and it is not possible to predict the structure or physical properties of a zeolite to be obtained from the raw materials or synthesis conditions. Therefore, in order to obtain a target zeolite, it is necessary to actually synthesize the zeolite. The synthesis conditions of an AFX zeolite are also unpredictable, and the following are production methods for AFX zeolites that have been reported in the past.
For example, in Patent Document 1, an AFX zeolite obtained by using a quinuclidine derivative as an organic structure directing agent (referred to as “SDA” hereafter) is disclosed as SSZ-16.
Types of SSZ-16 obtained using different SDAs and raw materials than those described in Patent Document 1 have been disclosed by multiple inventors (Patent Documents 2 and 3, Non-Patent Documents 1 to 4).
In Non-Patent Document 1, SSZ-16 having an SiO2/Al2O3 ratio of 9 is disclosed. This disclosed SSZ-16 is a crystal having many defects and does not have a good particle shape. In addition, in Non-Patent Document 2, an SCR reaction using a copper ion-exchanged substance obtained by ion-exchanging SSZ-16 having an SiO2/Al2O3 ratio of 9 with copper is investigated. It is disclosed that this SSZ-16 has good initial activity and has high durability with respect to treatment at temperatures with a relatively small thermal load, that is, in a hydrothermal atmosphere at 750° C.
In Patent Document 3 and Non-Patent Documents 3 and 4, SSZ-16 having a high SiO2/Al2O3 ratio is disclosed.
In Non-Patent Document 3, SSZ-16 having an SiO2/Al2O3 ratio of 33.4 is disclosed. On the other hand, it is disclosed that an AFX zeolite that has an SiO2/Al2O3 ratio other than 33.4 cannot be obtained. In addition, in Non-Patent Document 4, it is disclosed that an AFX zeolite is obtained only when a Y-type zeolite is used as a raw material.